Seminar On Underwater Welding -Report and ppt Download

INTRODUCTION TO UNDERWEAR WELDING

Underwater welding is an important tool for underwater fabrication works. In 1946, special waterproof electrodes were developed in Holland by ËœVander Willingen’â„¢. In recent years the number of offshore structures including oil drilling rigs, pipelines, platforms are being installed significantly. Underwater welding is a type of welding which takes place underwater.In underwater welding, the environment around the welder is wet. and uses welding equipment which has been customized for wet environment,commonly use under water techniques are hyperbaric enclosure welding, wet Underwater-welding, high pressure water jet welding, other welding processes: friction welding, resistance welding, arc welding, tig welding, mig welding, oxyacetylene welding, electron beam welding, laser beam welding,and main risks for the welder performing Underwater-welding are the potential for electric shock,and the possibility of producing in the arc mixtures of hydrogen and oxygen in pockets, which might set up an explosion,and There are three main ways to perform Underwater-welding. One is to build an enclosure, a pit, around the place of repair and to pump away all the water: that amounts to prepare the conditions for normal welding in air, although the place may be deep under sea level. Another method of Underwater-welding consists in preparing an enclosure to be filled with gas (helium) under high pressure (hyperbaric) to push water back, and have the welder, fitted with breathing mask and other protective equipment, weld quite normally out of water but under pressure. The third is the wet Underwater-welding method, where no attempts are made to dry up the location of welding. Instead the power of the arc generates a bubble of a mixture of gases which lets metal melting and joining occur more or less normally, using specially covered electrodes to avoid that too much hydrogen be absorbed in the weld. The skilled welder must also be a diver, equipped for Underwater-welding, with all the extra equipment and protection a welder must use. There is also a less used method of Underwater-welding which features a special torch which sprays a cone of high pressure water, within which protective gas under pressure insulates the weld location from the water during welding.

Fig. Under water welding

CLASSIFICATION

Under water welding can be classified as :i. Wet welding ii. Dry welding

1) WET WELDING

Key technology for repairing marine structure

Welding is performed under water directly exposed to the wet environment

Complete insulation of the cables and hoses are essential in case to prevent the chance for electric shock

MMA (Manual Metal Arc) welding is commonly used process in the repair of offshore platforms.

PRINCIPLE OF OPERATION

The work is connected to the positive side of dc source and electrode to the negative

The two parts of the circuit are brought together and then slightly separated

An electric current occurs in the gap and causes a sustained spark which melts the bare metal forming a weld pool The flux covering the electrode melts to provide a shielding gas.

Arc burns in the cavity formed inside the flux covering, which is designed to burn slower than the metal barrel to the electrode

Advantages

The versatility and low cost.

Less costlier than dry welding.

Speed with which it is carried out

No enclosures so no time is lost for building.

Disadvantages

Rapid quenching of the weld metal by the surrounding water.

Welders working under water are restricted in manipulating arc.

Hydrogen embrittlement causes cracks.

Poor visibility due to water contaminance.

2) DRY WELDING

A chamber is created near the area to be welded and the welder does the job by staying inside the chamber.

It produces high quality weld joints .

The gas-tungsten arc welding process is used mostly for pipe works

Gas metal arc welding is the best process for this welding.

Scope of further developments

Hyper baric welding is well established and generally well researched.

Research being carried out for welding at a range of 500 to 1000m deep.

THOR-1 (Tig Hyperbaric Orbital Robot) is developed where diver performs pipe fitting, installs the tracks and orbital head on the pipe and rest process is automated.

APPLICATIONS

Offshore construction for tapping sea resources

Temporary repair work caused by collisions, unexpected accidents

Salvaging vessels sunk in the sea

Repair and maintenance of ships

Construction of large ships beyond the capacity of existing docks

CONCLUSION Alternatives which include clamped and grouted repairs (which may introduce unacceptably high loading on offshore structures) and the use of bolted flanges for the tie-ins are not necessarily and are not always satisfactory.